Cooling apparatus

ABSTRACT

A cooling apparatus which stably cools a target. The cooling apparatus includes a primary circuit that has a first heat exchanging section which is provided at a heat exchanger, and vaporizes a liquid-phase primary coolant to be a gas-phase primary coolant, and a condenser which condenses the gas-phase primary coolant to be the liquid-phase primary coolant, and lets the liquid-phase primary coolant flow to the first heat exchanging section from the condenser through a liquid piping and lets the gas-phase primary coolant flow to the condenser from the first heat exchanging section through a gas piping. The cooling apparatus further includes a secondary circuit having a second heat exchanging section, an expansion valve, an evaporator, and a compressor connected together by a coolant piping.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cooling apparatus for use in a refrigerator, a freezer, an ice making machine, an air-conditioning system and the like.

2. Description of the Related Art

As a cooling apparatus for use in a refrigerator, a freezer, an ice making machine, an air-conditioning system and the like, a so-called remote condenser type (also called separate type) cooling apparatus 10 having a compressor CM and an evaporator EP disposed in a main body unit 12 arranged indoor and having a condenser CD disposed in an external unit 14 arranged outdoor has been proposed (see, for example, Japanese Patent Application Laid-Open No. H8-200746), as shown in FIG. 6. The cooling apparatus 10 of this type has a disadvantage that the provision of the condenser CD which is a heat discharging part outdoor can suppress a temperature rise in the main body unit 12.

SUMMARY OF THE INVENTION

In an environment where an outdoor temperature is low, such as winter, the cooling apparatus 10 may have heat over discharged by the condenser CD, so that the pressure of a coolant cannot be held on the high pressure side from the outlet side of the compressor CM in a cooling circuit 11 having the compressor CM, the condenser CD, an expansion valve EV and the evaporator EP connected together by a coolant piping 16 to the inlet side of the expansion valve EV. That is, in the cooling circuit 11, when a pressure on the high pressure side falls to nullify a difference between the pressure on the high pressure side and the pressure on the low pressure side from the outlet side of the expansion valve EV to the inlet side of the compressor CM, cooling of a target object by the evaporator EP cannot be controlled well, excessively cooling the target object. The remote condenser type cooling apparatus 10 lacks the stability of the cooling function with respect to a change in outside temperature.

As a solution to the problem, the cooling apparatus 10 has a condensing pressure regulating valve 20 provided in the cooling circuit 11 to regulate the flow rate of the coolant circulating into the cooling circuit 11, thereby suppressing a pressure drop on the high pressure side in the cooling circuit 11. Specifically, the cooling apparatus 10 is provided with a bypass pipe 18 bypassing the condenser CD between the coolant piping 16 which connects the compressor CM to the condenser CD, and the coolant piping 16 which connects the condenser CD to the expansion valve EV, and the condensing pressure regulating valve 20 is interposed at the bypass pipe 18. When the outside temperature becomes low, the condensing pressure regulating valve 20 of the cooling apparatus 10 adjusts the coolant so that the coolant stays in the condenser CD to reduce the area of heat exchange between the coolant and outside air in the condenser CD, thereby reducing the amount of heat discharge from the condenser CD and holding the pressure on the high pressure side of the cooling circuit 11. However, the adjustment by the condensing pressure regulating valve 20 needs to increase the amount of the coolant to be filled in the cooling circuit 11 in order to secure the amount of the coolant staying in the condenser CD when the outside temperature drops. As the amount of the coolant to be filled in the cooling circuit 11 increases, a lot of the coolant sleeps in the compressor CM when the compressor CM is stopped, so that when the compressor CM is activated, the oil is likely to be discharged by oil foaming or the like, and the viscosity of the lubricant to be filled in the compressor CM drops, causing wearing or the like of the operational parts of the compressor CM. This may result in malfunction of the compressor CM. Further, it is necessary to provide a liquid receiver R in the cooling, apparatus 10 to store a large amount of coolant unnecessary when the outside temperature is high, thus complicating the configuration and leading to a cost increase.

Another problem is that when the cooling circuit 11 is provided with a bypass circuit 22 which directly supplies the coolant to the evaporator EP from the compressor CM to execute deicing or defrosting with a hot gas, a part of the hot gas may flow into the condenser CD to be liquefied because the condenser CD is connected to the outlet side of the compressor CM. It is pointed out that when the coolant stays in the compressor CM this way, the amount of the coolant circulating in the cooling circuit 11 decreases, reducing the hot-gas based deicing performance and lowering the ice making efficiency. Since the adjustment with the condensing pressure regulating valve 20 actively lets the coolant stay in the condenser CD when the outside temperature drops, as mentioned above, the hot-gas based deicing performance is impaired significantly in the cooling apparatus 10 which supplies the hot gas to the evaporator EP through the bypass circuit 22.

Accordingly, the present invention has been proposed to adequately solve the inherent problems of the cooling apparatus according to the related art, and it is an object of the invention to provide a cooling apparatus which stably operates even when the ambient temperature varies.

To overcome the problems and achieve the object, a cooling apparatus according to one aspect of the invention includes:

a primary circuit that has a first heat exchanging section which is provided at a heat exchanger, and vaporizes a liquid-phase coolant to be a gas-phase coolant, and a condenser which condenses the gas-phase coolant to be the liquid-phase coolant, and lets the liquid-phase coolant flow to the first heat exchanging section from the condenser through a liquid piping and lets the gas-phase coolant flow to the condenser from the first heat exchanging section through a gas piping;

a secondary circuit having a second heat exchanging section, a restriction section, an evaporator, and a compressor connected together by a coolant piping, the second heat exchanging section being provided at the heat exchanger independently of the first heat exchanging section and being cooled by heat exchange with the coolant flowing to the first heat exchanging section; and

a flow rate regulating section capable of regulating a flow rate of the liquid-phase coolant, and being interposed at the liquid piping.

Even when the ambient temperature changes, the cooling apparatus according to the present invention can suppress the influence of the temperature change on the secondary circuit, so that the secondary circuit can stably cool a target object.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a cooling apparatus according to a preferred embodiment of the present invention;

FIG. 2 is a schematic diagram showing a cooling apparatus according to a first modification;

FIG. 3 is a schematic diagram showing a cooling apparatus according to a second modification;

FIG. 4 is a schematic diagram showing a cooling apparatus according to a third modification;

FIG. 5 is a schematic diagram showing a cooling apparatus according to a fourth modification; and

FIG. 6 is a schematic diagram showing a conventional cooling apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A cooling apparatus of the present invention will now be described by way of a preferred embodiment referring to the accompanying drawings. For the sake of descriptive convenience, To avoid the redundant description, same reference numerals are given to those components in the preferred embodiment which are the same as the corresponding components of the cooling apparatus shown in FIG. 6.

Embodiment

As shown in FIG. 1, a cooling apparatus 30 according to the embodiment is a remote condenser type in which a condenser 36 is independently set at a location different from the location of a compressor CM or the like, and is used in a refrigerator, a freezer, an ice making machine, an air-conditioning system or the like. The cooling apparatus 30 has two independent circuits, a primary circuit 32 which discharges heat and a secondary circuit 34 which cools a target object to be cooled, and has the primary circuit 32 and the secondary circuit 34 thermally cascade-connected via a heat exchanger 38. In the cooling apparatus 30, the components of the primary circuit 32 are separately provided in a main body unit 12 and an external unit 14 arranged separate from the main body unit 12, and the secondary circuit 34 is provided in the main body unit 12.

The heat exchanger 38 has a first heat exchanging section 40 constituting the primary circuit 32 and a second heat exchanging section 42 which is formed as a separate system from the first heat exchanging section 40 and constitutes the secondary circuit 34. The heat exchanger 38 in use is of a plate type, for example. The heat exchanger 38 performs heat exchange between a primary coolant (coolant) flowing through the first heat exchanging section 40 and a secondary coolant (coolant) flowing through the second heat exchanging section 42 in such a way that the primary coolant absorbs heat from the secondary coolant while the secondary coolant discharges heat to the primary coolant.

The primary circuit 32 is configured so that the first heat exchanging section 40 provided in the heat exchanger 38 arranged in the main body unit 12 is connected to an air-cooling type-condenser 36 arranged in the external unit 14 provided separate from the main body unit 12 by a liquid piping 44 and a gas piping 46. The external unit 14 is provided with an air fan (not shown) to feed air to the condenser 36. As the primary coolant to be filled in the primary circuit 32, flon R134a, flon R404A, flon R410A, etc. are used. Particularly, a medium with a critical temperature of 60° C. or higher is preferable. A pump (flow rate regulating section) 48 is interposed at the liquid piping 44 to feed a liquid-phase primary coolant from the condenser 36 toward the first heat exchanging section 40 under pressure through the liquid piping 44. The pump 48 in use is of a type which can regulate the flow rate of the liquid-phase primary coolant. If the pump 48 is of a type which feeds the liquid-phase primary coolant under pressure with the rotation of a rotor or the reciprocative motion of a diaphragm or a plunger, for example, the flow rate is adequately adjusted by variably controlling the number of rotations or the number of reciprocations per hour or variably controlling the discharge resistance with the opening/closing of a valve body. The condenser 36 in use is a fin-and-tube type having a heat discharge duct (passage) 36 a whose linear portions extending horizontally are arranged zigzagged in the up and down direction, and a fin (not shown) connected to the heat discharge duct 36 a and made of a metal, such as aluminum or copper, which has an excellent thermal conductivity.

In the cooling apparatus 30 according to the embodiment, the external unit 14 is located lower than the main body unit 12, and the condenser 36 arranged in the external unit 14 is positioned lower than the first heat exchanging section 40 of the heat exchanger 38 arranged in the main body unit 12. In the positional relationship between the first heat exchanging section 40 and the condenser 36, the liquid piping 44 has a start end connected to the flow-out end of the heat discharge duct 36 a which is positioned at a lower portion of the condenser 36, and a terminal end connected to a lower portion of the first heat exchanging section 40. The gas piping 46 has a start end connected to an upper portion of the first heat exchanging section 40, and a terminal end connected to the flow-in end of the heat discharge duct 36 a which is positioned at an upper portion of the condenser 36. Formed in the primary circuit 32 is a primary-coolant circulation cycle in which a liquid-phase primary coolant is vaporized to be a gas-phase primary coolant by the first heat exchanging section 40, the gas-phase primary coolant is supplied to the condenser 36 from the first heat exchanging section 40 through the gas piping 46 and is condensed to be a liquid-phase primary coolant by the condenser 36, and the liquid-phase primary coolant is fed from the condenser 36 to the first heat exchanging section 40 through the liquid piping 44 under pressure by the pump 48.

In the cooling apparatus 30, the pump-out amount of the pump 48 is variably controlled according to a change in the heat discharge performance of the condenser 36 caused by a change in the ambient temperature of the external unit 14, thereby regulating the flow rate of the primary coolant circulating in the primary circuit 32. In the cooling apparatus 30, driving or stopping of the pump 48 is controlled based on the result of temperatures measured by temperature measuring sections 50, 52 provided in the condenser 36. When the ambient temperature of the external unit 14 drops and the heat discharge performance of the condenser 36 increases, the cooling apparatus 30 performs control to reduce the pump-out amount of the pump 48 to reduce the flow rate of the primary coolant circulating into the primary circuit 32. When the ambient temperature becomes lower so that the heat discharge performance of the condenser 36 becomes excessive, the cooling apparatus 30 performs control to stop the pump 48 to stop circulation of the primary coolant in the primary circuit 32. When the ambient temperature of the external unit 14 rises so that the heat discharge performance of the condenser 36 is reduced, the cooling apparatus 30 performs control to increase the pump-out amount of the pump 48, thereby increasing the flow rate of the primary coolant circulating into the primary circuit 32. Apparently, the cooling apparatus 30 is configured in such a way as to change the flow rate of the primary coolant from the pump 48 in inverse proportion to a change in the heat discharge performance of the condenser 36 which is acquired based on the temperature measured by a temperature sensor TH which measures the ambient temperature.

The drive or stop control of the pump 48 will be described specifically. A pair of temperature measuring sections 50, 52 set apart from each other in the flow direction of the primary coolant in the heat discharge duct 36 a are provided in the condenser 36 along the heat discharge duct 36 a, and measures the temperature of the primary coolant flowing through the heat discharge duct 36 a. One temperature measuring section (hereinafter “first temperature measuring section”) 50 is arranged in the condenser 36 at the same height as the inlet of the pump 48 or at a position higher than the inlet thereof. On the other hand, the other temperature measuring section (hereinafter “second temperature measuring section”) 52 is provided between the flow-in end of the heat discharge duct 36 a in the condenser 36 and the location of the first temperature measuring section 50 in the heat discharge duct 36 a. The second temperature measuring section 52 is located above the first temperature measuring section 50 and at an expected position in the heat discharge duct 36 a of the condenser 36 where the gas-phase primary coolant flowing from the gas piping 46 and the liquid-phase primary coolant which is the gas-phase primary coolant condensed by heat exchange with the ambient atmosphere coexist (stable balanced state) and become saturated, or in the vicinity of the expected position. That is, the second temperature measuring section 52 measures the saturation temperature of the coolant circulation cycle in the primary circuit 32.

The cooling apparatus 30 is configured to compare the temperature measured by the first temperature measuring section 50 with the temperature measured by the second temperature measuring section 52, and allow the pump 48 to be driven when the temperature measured by the first temperature measuring section 50 is lower than a value obtained by subtracting a preset allowance value from the temperature measured by the second temperature measuring section 52. The cooling apparatus 30 stops the active pump 48 or keeps the stop state of the inactive pump 48 when the temperature measured by the first temperature measuring section 50 is equal to or higher than the value obtained by subtracting the preset allowance value from the temperature measured by the second temperature measuring section 52. The allowance value is a value set to protect the pump 48, and is set between 0° C. and several ° C. That is, the allowance value may not be set depending on a condition. A change in the heat discharge performance of the condenser 36 caused by a change in ambient temperature may be calculated from the temperatures measured by the first temperature measuring section 50 and the second temperature measuring section 52.

The secondary circuit 34 is configured so that the compressor CM which compresses a gas-phase secondary coolant, the second heat exchanging section 42 which takes away heat from the gas-phase secondary coolant to be condensed and liquefied, an expansion valve (restriction section) EV which drops the pressure of a liquid-phase secondary coolant, and the evaporator EP which vaporizes the liquid-phase secondary coolant are connected together by a coolant piping 16. As the primary coolant to be filled in the secondary circuit 34, flon R134a, flon R404A, flon R410A, flon R290, flon R600a or the like is used. Particularly, a medium which can be condensed and vaporized within the temperature range of 0° C. to 60° C. is preferable. In the secondary circuit 34, the secondary coolant is forcibly circulated in the order of the compressor CM, the second heat exchanging section 42, the expansion valve EV, the evaporator EP and the compressor CM by a differential pressure produced by compression of the secondary coolant by the compressor CM with the expansion valve EV being the boundary, so that a target object is cooled by the evaporator EP under the actions of the individual components. In the second heat exchanging section 42, the gas-phase secondary coolant flowing from the compressor CM is subjected to heat exchange with the liquid-phase primary coolant flowing through the first heat exchanging section 40 while passing through the duct, and its heat is taken away to be condensed and liquefied to become a liquid-phase secondary coolant.

Operation of Embodiment

The operation of the cooling apparatus 30 according to the embodiment will be described next. In the primary circuit 32 of the cooling apparatus 30, a gas-phase primary coolant discharges heat to be liquefied while flowing through the heat discharge duct 36 a of the condenser 36 to have phase transition from a gas-phase primary coolant to a liquid-phase primary coolant. The liquid-phase primary coolant is pumped out from the pump 48, flows into the first heat exchanging section 40 through the liquid piping 44, is vaporized by heat exchange with the gas-phase secondary coolant flowing through the second heat exchanging section 42 to have phase transition from a liquid-phase primary coolant to a gas-phase primary coolant. Then, the gas-phase primary coolant flows into the condenser 36 through the gas piping 46. In this manner, the circulation cycle of the primary coolant between the condenser 36 and the first heat exchanging section 40 is repeated.

Meanwhile, in the secondary circuit 34, a gas-phase secondary coolant is compressed by the compressor CM, flows into the second heat exchanging section 42 through the coolant piping 16, is cooled by the primary coolant flowing through the first heat exchanging section 40 to be condensed and liquefied to have phase transition to a liquid-phase secondary coolant. The liquid-phase secondary coolant is depressurized by the expansion valve EV, absorbs surrounding heat in the evaporator EP to be expanded and vaporized at a burst, so that the target object is cooled by the evaporator EP. The gas-phase secondary coolant vaporized by the evaporator EP repeats a forced circulation cycle of being fed back to the compressor CM through the coolant piping 16.

When the ambient temperature of the external unit 14 drops and the heat discharge performance of the condenser 36 is enhanced, the cooling apparatus 30 reduces the pump-out amount of the liquid-phase primary coolant by the pump 48 to reduce the flow rate of the coolant circulating into the primary circuit 32, thereby increasing the amount of the primary coolant staying in the condenser 36. The heat discharge performance of the condenser 36 is acquired from the result of measuring the ambient temperature by the temperature sensor TH. As the primary coolant staying in the condenser 36 increases, the area of heat exchange with the ambient temperature in the condenser 36 decreases, so that the balance of the amounts of heat exchange between the low-temperature ambient atmosphere and the primary coolant is adjusted. As the ambient temperature of the external unit 14 rises to reduce the heat discharge performance of the condenser 36, the pump-out amount of the liquid-phase primary coolant by the pump 48 increases to increase the flow rate of the coolant circulating into the primary circuit 32. This reduces the amount of the primary coolant staying in the condenser 36. As the amount of the primary coolant staying in the condenser 36 reduces, the area of heat exchange with the ambient temperature in the condenser 36 increases, so that the balance of the amounts of heat exchange between the high-temperature ambient atmosphere and the primary coolant is adjusted. That is, even when the ambient temperature of the external unit 14 changes, the heat discharge performance of the condenser 36 can be adjusted adequately. Accordingly, the performance of the first heat exchanging section 40 of cooling the second heat exchanging section 42 can be kept properly, the temperature change does not influence the condensation and liquefaction of the gas-phase secondary coolant in the second heat exchanging section 42 of the secondary circuit 34. As the differential pressure between the high pressure side and the low pressure side is adequately held in the secondary circuit 34, it is possible to avoid over-cooling of the target object in the evaporator EP. The cooling apparatus 30 shows stable cooling capability which is not influenced by a change in ambient temperature.

When the cooling apparatus 30 is installed in an ice making machine, for example, a bypass circuit (not shown) which directly supplies a hot gas to the evaporator EP from the compressor CM without going through the second heat exchanging section 42 and the expansion valve EV is provided, so that in an ice making operation, the secondary coolant circulates the compressor CM, the second heat exchanging section 42, the expansion valve EV and the evaporator EP and an ice making section (not shown) or a target object is cooled in the evaporator EP. In a deicing operation, a hot gas is supplied to the evaporator EP from the compressor CM through the bypass circuit to heat the evaporator EP, thereby heating the ice making section. In the deicing operation, as the hot gas to be supplied to the evaporator EP becomes hotter and has a higher pressure, the deicing performance becomes higher, so that it is required not to reduce the pressure on the high pressure side in the secondary circuit 34. In the ice making operation, on the other hand, there should be a differential pressure high enough for allowing the liquid-phase secondary coolant to flow to the expansion valve EV, the differential pressure demanded between the high pressure side and the low pressure side in the secondary circuit 34 is lower than that in the deicing operation. As described above, the secondary circuit 34 is merely thermally connected to the primary circuit 32 at the heat exchanger 38, and is independent of the primary circuit 32 as a coolant passage, and a change in the differential pressure between the high pressure side and the low pressure side in the secondary circuit 34 can be suppressed by adjusting the heat discharge performance of the primary circuit 32 according to a change in the ambient temperature of the external unit 14. In addition, the cooling apparatus 30 can adequately adjust the general balance of the cooling apparatus 30 according to the operational conditions or the like by positively adjusting the flow rate of the coolant regardless of the ambient temperature of the external unit 14 by using the pump 48. Specifically, in the ice making operation, the pump-out amount of the pump 48 is controlled down to suppress the heat discharge performance of the secondary circuit 34 by means of the primary circuit 32, thereby lowering the pressure on the high pressure side in the secondary circuit 34 and thus improving the cooling performance of the evaporator EP. In the deicing operation, the pump-out amount of the pump 48 is controlled up to enhance the heat discharge performance of the secondary circuit 34 by means of the primary circuit 32, thereby increasing the pressure on the high pressure side in the secondary circuit 34 and thus improving the deicing performance of the evaporator EP.

When the pump 48 stops in the cooling apparatus 30 to stop the circulation of the primary coolant in the primary circuit 32, heat discharge of the secondary circuit 34 by the primary circuit 32 is not performed. That is, stopping the pump 48 can make the secondary circuit 34 uninfluenced at all by a change in temperature in the external unit 14 in the cooling apparatus 30. Even when the ambient temperature of the external unit 14 is low, therefore, the temperature on the high pressure side of the secondary circuit 34 can be kept high, so that the ice making efficiency can be improved by shortening the deicing operation. This can suppress an overloading of the mechanism section, such as a rotary knife or a motor which drives the rotary knife even when the cooling apparatus 30 is applied to an auger-type ice-making machine with no hot gas circuit. The load on the mechanism section can be further reduced by adjusting the heat discharge performance of the secondary circuit 34 with the primary circuit 32 by adjusting the flow rate of the pump 48 according to the load on the mechanism section detected by a sensor.

The cooling apparatus 30 does not require that the secondary coolant should stay in the secondary circuit 34 to cope with a change in the ambient temperature of the external unit 14. This makes it possible to reduce the amount of the secondary coolant to be filled in the secondary circuit 34. Reducing the amount of the secondary coolant to be filled in the secondary circuit 34 can avoid oil discharge originated from oil foaming or the like, which occurs when the compressor CM is started, and wear-out or the like of the operational parts of the compressor CM originated from a reduction in the viscosity of the lubricant filled in the compressor CM, and improve the reliability of the compressor CM. It is also possible to omit a receiver for retaining the secondary coolant from the secondary circuit 34, thus simplifying the structure of the secondary circuit 34.

As the cooling apparatus 30 does not have the compressor CM in the primary circuit 32, oil such as the lubricant in the compressor CM is not present in the primary circuit 32, and an oil film which interferes with heat exchange of the secondary coolant does not adhere to the first heat exchanging section 40 or the heat discharge duct 36 a of the condenser 36. The cooling apparatus 30 is therefore excellent in the heat exchange efficiency of the heat exchanger 38 and heat discharge performance in the condenser 36. The conventional cooling apparatus 10 described referring to FIG. 6 brings about a problem such that because the lubricant flowing out from the compressor CM circulates in the cooling circuit 11 together with the coolant, the lubricant in the compressor CM becomes short if the coolant piping 16 becomes longer with the main body unit 12 and the external unit 14 set apart from each other. In the cooling apparatus 30 according to the embodiment, by way of contrast, the secondary circuit 34 is provided entirely in the main body unit 12, and is independent of the primary circuit 32, so that the conventional problem does not arise even when the location of the main body unit 12 is set far from the location of the external unit 14. That is, the cooling apparatus 30 has a higher degree of freedom in the set locations of the main body unit 12 and the external unit 14.

The following will describe the drive control of the pump 48 based on the temperatures measured by the first temperature measuring section 50 and the second temperature measuring section 52. The second temperature measuring section 52 is set at a position corresponding to the expected position in the heat discharge duct 36 a of the condenser 36 where the gas-phase primary coolant and the liquid-phase primary coolant are balanced out, and the first temperature measuring section 50 measures the saturation temperature of the primary coolant. The first temperature measuring section 50 is set below the second temperature measuring section 52 set at a position corresponding to the expected position in the heat discharge duct 36 a of the condenser 36 where the gas-phase primary coolant and the liquid-phase primary coolant are balanced out, and will measure the temperature of the over-cooled liquid-phase primary coolant. The temperature of the over-cooled liquid-phase primary coolant becomes lower than the saturation temperature. That is, when the temperature measured by the first temperature measuring section 50 becomes lower than the temperature measured by the second temperature measuring section 52 in the comparison thereof with each other, it is confirmed that the liquid-phase primary coolant is filled up to the set location of the first temperature measuring section 50 in the heat discharge duct 36 a. Because the first temperature measuring section 50 is located at or higher the inlet side of the pump 48, it can be determined that the height of the retention of the liquid-phase primary coolant in the liquid piping 44 has reached at least the inlet of the pump 48 if the liquid-phase primary coolant is filled in the heat discharge duct 36 a up to the set location of the first temperature measuring section 50. When the temperature measured by the first temperature measuring section 50 becomes higher than the temperature measured by the second temperature measuring section 52, on the other hand, it is confirmed that the liquid-phase primary coolant is not filled up to the set location of the first temperature measuring section 50 in the heat discharge duct 36 a, and the height of the retention of the liquid-phase primary coolant in the liquid piping 44 has not reached the inlet of the pump 48. If the liquid-phase primary coolant is not filled up to the inlet of the pump 48, control is performed to allow driving of the pump 48 with the liquid-phase primary coolant filled up to the inlet of the pump 48, making it possible to avoid cavitation originated from suction of the gas-phase primary coolant by the pump 48 and prevent malfunction of the pump 48. The precision in the regulation of the flow rate with the pump 48 can be improved. In the embodiment, the allowance value is set to increase the probability of the determination.

(Modifications)

The present invention is not limited to the configuration of the embodiment, and may be modified in the following forms. In modifications, the configuration of the embodiment is employed unless otherwise specified.

-   (1) In a cooling apparatus 60 according to a first modification     shown in FIG. 2, an external unit 14 is arranged above a main body     unit 12, and a condenser 36 arranged in the external unit 14 is     positioned above a first heat exchanging section 40 of a heat     exchanger 38 arranged in the main body unit 12. In the positional     relationship between the first heat exchanging section 40 and the     condenser 36, a liquid piping 44 has a start end connected to the     flow-out end of a heat discharge duct 36 a which is positioned at a     lower portion of the condenser 36, and a terminal end connected to     an upper portion of the first heat exchanging section 40. A gas     piping 46 has a start end connected to a lower portion of the first     heat exchanging section 40, and a terminal end connected to the     flow-in end of the heat discharge duct 36 a which is positioned at     an upper portion of the condenser 36. In a primary circuit 62, a     liquid-phase primary coolant is vaporized to be a gas-phase primary     coolant by the first heat exchanging section 40, the gas-phase     primary coolant is naturally supplied to the condenser 36 from the     first heat exchanging section 40 through the gas piping 46 due to     the differential pressure between the first heat exchanging section     40 and the condenser 36 and the difference in the density of the     primary coolant therebetween. In the primary circuit 62, a gas-phase     primary coolant is condensed to be a liquid-phase primary coolant by     the condenser 36, and the liquid-phase primary coolant naturally     flows down to the first heat exchanging section 40 from the     condenser 36 due to the differential pressure between the first heat     exchanging section 40 and the condenser 36 and the difference in the     density of the primary coolant therebetween. As apparent from the     above, a natural convection cycle of the primary coolant is formed     in the primary circuit 62 according to the first modification.     Further, a flow rate regulating valve (flow rate regulating section)     64 which can regulate the flow rate of the liquid-phase primary     coolant flowing through the liquid piping 44 is interposed at the     liquid piping 44.

In the cooling apparatus 60 according to the first modification, the opening/closing of the flow rate regulating valve 64 is controlled according to a change in the heat discharge performance of the condenser 36 which is acquired from a change in the ambient temperature of the external unit 14 which is measured by a temperature sensor TH. That is, the cooling apparatus 60 is configured so that when the ambient temperature of the external unit 14 drops to increase the heat discharge performance of the condenser 36, the degree of opening of the flow rate regulating valve 64 is restricted to reduce the flow rate of the primary coolant circulating into the primary circuit 32. When the heat discharge performance of the condenser 36 becomes excessive as a consequence of a reduction in ambient temperature, the cooling apparatus 60 closes the flow rate regulating valve 64 to stop the circulation of the primary coolant in the primary circuit 32. Then, when the ambient temperature of the external unit 14 rises to reduce the heat discharge performance of the condenser 36, the cooling apparatus 60 increases the degree of opening of the flow rate regulating valve 64 to increase the flow rate of the primary coolant circulating into the primary circuit 32. Apparently, the cooling apparatus 60 can adequately adjust the performance of the first heat exchanging section 40 to cool a second heat exchanging section 42 by changing the flow rate of the primary coolant by means of the flow rate regulating valve 64 in inverse proportion to a change in the heat discharge performance of the condenser 36, and does not therefore influence the action of the second heat exchanging section 42 to condense the gas-phase secondary coolant in the secondary circuit 34.

The primary circuit 62 of the first modification is provided with a rise-up portion 44 a between the outlet side of the condenser 36 and the inlet side of the flow rate regulating valve 64 in the liquid piping 44. The rise-up portion 44 a is a part of the liquid piping 44 rising upward. A point of inflection of the rise-up portion 44 a from the upward inclination to downward inclination is set higher than the height of the start end of the liquid piping 44 to be connected to the flow-out end of the heat discharge duct 36 a of the condenser 36 and lower than the flow-in end of the heat discharge duct 36 a. That is, the provision of the rise-up portion 44 a at the liquid piping 44 can permit the liquid-phase primary coolant to stay in the heat discharge duct 36 a of the condenser 36 up to the height of the point of inflection of the rise-up portion 44 a, the staying liquid-phase primary coolant can be over-cooled by feeding air using an air fan. Therefore, the liquid-phase primary coolant which does not contain a gas-phase primary coolant can be allowed to flow down to the flow rate regulating valve 64, thus facilitating adjustment of the flow rate of the coolant circulating into the primary circuit 62 by opening/closing the flow rate regulating valve 64. The supply of the liquid-phase primary coolant which contains a gas-phase primary coolant to the flow rate regulating valve 64 makes it difficult to adjust the degree of opening of the flow rate regulating valve 64 and the flow rate of the primary coolant in the primary circuit 62 due to the influence of the gas-phase primary coolant.

-   (2) A cooling apparatus 70 according to a second modification shown     in FIG. 3 is configured to have a liquid tank 72 added between a     condenser 36 in a primary circuit 71 and a first heat exchanging     section 40. The liquid tank 72 is located above the first heat     exchanging section 40. The liquid tank 72 and the condenser 36 are     connected together by a first liquid piping 73 and a first gas     piping 74, and the liquid tank 72 and the first heat exchanging     section 40 are connected together by a second liquid piping 75 and a     second gas piping 76. The first liquid piping 73 has a start end     connected to the flow-out end of a heat discharge duct 36 a     positioned at a lower portion of the condenser 36, and a terminal     end connected to a lower portion of the liquid tank 72, so that a     liquid-phase primary coolant is fed out to the liquid tank 72 from     the condenser 36 under pressure through the first liquid piping 73     by a pump 48. The first gas piping 74 has a start end connected to     an upper portion of the liquid tank 72, and a terminal end connected     to the flow-in end of the heat discharge duct 36 a positioned at an     upper portion of the condenser 36. The second liquid piping 75 has a     start end connected to the lower portion of the liquid tank 72 and a     terminal end connected to an upper portion of the first heat     exchanging section 40, so that a liquid-phase primary coolant     naturally flows down from the liquid tank 72 through the second     liquid piping 75 inclined downward. The second gas piping 76 has a     start end connected to a lower portion of the first heat exchanging     section 40, and a terminal end connected to the upper portion of the     liquid tank 72. A flow rate regulating valve 64 capable of     regulating the flow rate of the liquid-phase primary coolant flowing     down in the second liquid piping 75 is interposed at the second     liquid piping 75. In the cooling apparatus 70 according to the     second modification, the primary circuit 71 cain perform regulation     of the flow rate with the pump 48 and regulation of the flow rate     with the flow rate regulating valve 64. Because the cooling     apparatus 70 according to the second modification has the liquid     tank 72 provided in the primary circuit 71, a large amount of the     primary coolant circulating into the primary circuit 71 can be set. -   (3) Although the descriptions of the embodiment, and the first and     second modifications have been given of a case where the condenser     36 and the first heat exchanging section 40 in the primary circuit     32, 62, 71 has a one-to-one correlation, a plurality of (two in     FIG. 4) first heat exchanging sections 40 may be connected to a     single condenser 36 as in a cooling apparatus 80 according to a     third modification shown in FIG. 4 or a cooling apparatus 90     according to a fourth modification shown in FIG. 5. That is, a     plurality of main body units 12 can share a single external unit 14     having a single condenser 36. -   (4) While an expansion valve is used as a restriction section for     reducing the pressure, a capillary tube may be used instead. 

1. A cooling apparatus comprising: a primary circuit that has a first heat exchanging section which is provided at a heat exchanger, and vaporizes a liquid-phase coolant to be a gas-phase coolant, and a condenser which condenses the gas-phase coolant to be the liquid-phase coolant, and lets the liquid-phase coolant flow to the first heat exchanging section from the condenser through a liquid piping and lets the gas-phase coolant flow to the condenser from the first heat exchanging section through a gas piping; a secondary circuit having a second heat exchanging section, a restriction section, an evaporator, and a compressor connected together by a coolant piping, the second heat exchanging section being provided at the heat exchanger independently of the first heat exchanging section and being cooled by heat exchange with the coolant flowing to the first heat exchanging section; and a flow rate regulating section capable of regulating a flow rate of the liquid-phase coolant, and being interposed at the liquid piping.
 2. The cooling apparatus according to claim 1, wherein a pump which feeds the liquid-phase coolant toward the first heat exchanging section under pressure and is capable of regulating a flow rate of the liquid-phase coolant to be fed under pressure is used as the flow rate regulating section.
 3. The cooling apparatus according to claim 2, wherein a pair of temperature measuring sections set apart from each other in a flow direction of a coolant in a passage thereof are provided in the condenser along the passage, and driving of the pump is controlled based on a difference between temperatures measured by the pair of temperature measuring sections.
 4. The cooling apparatus according to claim 1, wherein the condenser is arranged at a position higher than the first heat exchanging section, and a flow rate regulating valve capable of regulating a flow rate of the liquid-phase coolant flowing in the liquid piping is used as the flow rate regulating section.
 5. The cooling apparatus according to claim 4, wherein a rise portion is provided at the liquid piping between an outlet side of the condenser and the flow rate regulating valve. 